2．The movies just wouldn't be the same without the warm buttery taste of popcorn．Amazingly，this delicious treat started its life as a corn kernel （玉米粒），not just from any corn．Popcorn is a type of sweet corn that was originally grown in Mexico and spread to China，India and elsewhere．It is the only kind of corn that will pop．Today，most of the world's popcorn is grown in the United States．
Every popcorn kernel contains a tiny drop of water，surrounded by soft starch （淀粉）．When the popcorn is heated，the water turns into steam．This puts pressure on the surrounding hard kernel，forcing it to explode．The soft starch increases about 40times in size as the corn kernel turns itself inside out．
In the 1500s popcorn was an important food source for the Aztec Indians of central and southern Mexico．But it wasn't only food．It was also used in ceremonies or on red dresses and in necklaces．By the time the Europeans arrived in America，popcorn had spread through most of the American Indians．
Some early American settlers ate popcorn with cream and sugar for breakfast．But it wasn't until the late 1800s that popcorn became popular．The demand for popcorn increased and farmers began farming popcorn．The first mobile popping machine was invented in 1885，and popcorn was sold by street sellers much like hot dogs that are sold today．
During the Great Depression of the 1930s，the popcorn business still thrived as people could still afford it．Then in the 1950s television arrived and popcorn consumption decreased．People stayed home and stopped going to the theatre．But the link between movies and popcorn had already existed．Soon people began making popcorn at home on the stove and，later，microwave popcorn was introduced．Today the movies have regained popularity and popcorn has once again become the favorite．
32．Popcorn was first planted inD．
A．China
B．America
C．India
D．Mexico
33．Why does the corn kernel pop when heated？B
A．Because it is covered with soft starch．
B．Because the pressure inside is too big．
C．Because the starch becomes bigger in size．
D．Because there is water inside the kernel．
34．We can know from the passage thatA．
A．popcorn began to be farmed in the late 1800s
B．popcorn was only a kind of food in the 1500s
C．hot dogs used to be sold by street sellers
D．people stop eating popcorn while watching movies now
35．The underlined word"thrived"in the fifth paragraph probably means"D"．
A．started to disappear
B．was seriously affected
C．suffered a lot
D．developed very well．
